1. Field of the Invention
The present invention relates to viewers using wavelengths outside the visible spectrum. More specifically, the invention provides a viewer that combines an image transmitted using wavelengths outside the visible spectrum, for example, thermal infrared, with a visible light image.
2. Description of the Related Art
Although other devices for combining visible light images with images formed in other wavelengths have been proposed, there remains a need for such device that minimizes parallax and image shift to a degree to be sufficient for use as a firearms sight, or for use in front of a daytime telescopic sight.
U.S. Patent Application Publication Number US 2003/0206338 A1, disclosing an invention by L. G. Cook and published on Nov. 6, 2003, discloses an optical system for simultaneous imaging of long wave infrared and millimeter wave radiation. The system includes a primary mirror, a Mangin secondary mirror structured to receive light reflected from the primary mirror, and an immersion lens structured to focus the energy received from the secondary mirror. The immersion lens effectively decreases the wavelength of the millimeter wave radiation, allowing a smaller detector to collect the same amount of radiation as would a larger detector in air.
U.S. Pat. No. 6,909,539, issued to R. J. Korniski, et al. on Jun. 21, 2005, discloses a system for combining multiple energy bands to improve scene viewing. The device includes an objective lens that is optimized for both visible/near infrared wavelengths and infrared wavelengths. After passing through the objective lens, visible light is directed towards an image intensifier, while infrared light is transmitted to an IRFPA. The electronic digital image resulting from the infrared image is displayed on a display to a beam combiner to which the intensified image is also displayed. The combined image is displayed to a user's eye. The preferred embodiments are a monocular or binoculars. The patent does not disclose any means for resisting image shift due to expansion and contraction of the various components due to temperature change, or due to the night vision device receiving an impact, a necessary feature for any night vision device used in conjunction with a weapon. A similar device is disclosed in U.S. Pat. No. 6,646,799, issued to the same inventors on Nov. 11, 2003.
U.S. Pat. No. 6,094,302, issued to D. Bergstedt on Jul. 25, 2000, discloses an infrared viewing device having a parallel channel for visible light. The infrared image and visible light image are displayed to the user separately.
U.S. Pat. No. 6,020,994, issued to L. G. Cook on Feb. 1, 2000, discloses a multi-functional viewer providing for infrared viewing, direct visible viewing, CCD based visible TV viewing, and laser range finding. Mode switching mirrors are used to direct the desired image to a single eye piece. No means for combining images is disclosed.
U.S. Pat. No. 5,973,315, issued to M. R. Saldana et al. on Oct. 26, 1999, discloses a day/night observation, ranging and sighting device. Light passing through the objective lens passes through a beam splitter that permits red and orange light to pass through the beam splitter to an image intensifier, and reflects other visible light to a series of lens elements. About 70% to 80% of the light admitted through the objective lens is directed away from the image intensifier. The visible light image and intensified image are combined using a beam combiner, before passing through an aiming reticle and other lens elements towards the eye piece. A laser range finder is also included. A similar device is disclosed in U.S. Pat. No. 5,892,617, issued to R. E. Wallace on Apr. 6, 1999. Neither of these patents discloses any means for resisting image shift due to expansion and contraction of the various components due to temperature changes, or to impact on a device.
U.S. Pat. No. 5,933,277, issued to J. R. Truxell et al. on Aug. 3, 1999, discloses an imaging system combining visible and non-visible electromagnetic radiation for enhanced vision. Electromagnetic radiation entering the imaging system is directed towards a diffraction grating, which reflects the different wavelengths at different angles to the appropriate detectors. The electric signal output from the detectors is transmitted to processing electronics which combine the data from the two scanned signals to produce an enhanced visible image. This patent does not disclose an image combining method having sufficient resolution for use with firearm sights.
U.S. Pat. No. 5,781,336, issued to B. Coon et al. on Jul. 14, 1998, discloses the use of the combination of a magnesium oxide lens and a calcium fluoride lens for multi-spectral imaging systems utilizing both the visible and infrared spectrums.
U.S. Pat. No. 5,157,548, issued to L. Monnier et al. on Oct. 20, 1992, discloses an optical device combining either a direct daylight view or an intensified image with an image generated by an image generator. No method of combining visible light image with an image outside the visible spectrum is disclosed.
U.S. Pat. No. 5,035,472, issued to C. L. Hansen on Jul. 30, 1991, discloses an integrated multi-spectral man portable weapon sight. The sight emits visible, near infrared, and far infrared light through a single objective lens using beam splitters to separate the light into near infrared, far infrared, and visible light. No means of combining visible light image with an image formed in another wavelength is disclosed.
U.S. Pat. No. 5,841,574, issued to G. W. Willey on Nov. 24, 1998, discloses a multi-spectral decentered catadioptric optical system. The entrance pupil of the lens is not concentric with the lens. The small residual obscuration enters the circular pupil from one side, instead of being located in the center.
Accordingly, there is a need for a system of combining a visible light image with an image from a different wavelength, having sufficient resolution and elimination of parallax for use in conjunction with a firearm sight. There is a further need for such a device that may be placed in front of a firearm sight, without changing the relationship between point of aim and the point of impact of the firearm sight.